Illustration: Brendan Lynch/AxiosSilicon Valley is pushing senators to follow the House's lead in reviving a favorable tax benefit that disappeared several years ago.Why it matters: This could change the math for a slew of startups, and even Big Tech companies.The big picture: U.S. companies currently are unable to fully deduct many software development and other R&D costs, including certain employee salaries, from their taxable income.That's because of a change made to Section 174 of the tax co...